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AM26C31: Unexpected behavior

Zeming Kong
Expert 3515 points
Part Number: AM26C31
Other Parts Discussed in Thread: AM26C32,

Hi team,

My customer found an unexpected behavior.

a small voltage and a very short pulse occurred in 1A of AM26C32 when G/ of AM26C31 was L=>H during VCC startup.

Could you let me know what is the reason? And how to solve it?

Can we disable the device before VCC startup to prevent this?

Best,
Zeming

 

  • 0
    Guru 316690 points

    To disable the driver during startup, you must keep G low and /G high.

  • 0
    TI__Guru 52172 points

    Hi Zemming,

    The device is enabled at start up as /G is starting at low - if pin 4 is high or pin 12 is low during start up the driver will start enabled.

    Is /G pulled up to device VCC or is there another signal being sent to /G? 

    Please let me know.

    Best,

    Parker Dodson

  • 0 in reply to Parker Dodson
    TI__Expert 3515 points

    Hi Parker,

    The customer wants to pull up /G with VCC, is it okay?

     And do you mean this behavior is expected because the device is enabled during startup?

    Best,
    Zeming

  • 0 in reply to Zeming Kong
    TI__Guru 52172 points

    Hi Zeming,

    Is the customer already tying /G to VCC through a resistor? If so what is the resistance value being used? As this should help prevent the issue being seen by customer - or are they doing a direct connect to VCC?

    What I am saying, sorry if I wasn't clear, is that if the /G is low at startup the device will start active - it seems the device starts enabled and then is disabled during the start up - which is what the voltage signal on "A" seems to imply. As when the device is disabled the output will be high z. I am not sure on the states of the input pins at start up - but if /G can be high or ~equal to VCC during start up the device should remain in its disabled state until /G is low or G is driven high. 

    Best,

    Parker Dodson